Functionalized carbon nanotube-polymer composites and interactions with radiation

ABSTRACT

The present invention involves the interaction of radiation with functionalized carbon nanotubes that have been incorporated into various host materials, particularly polymeric ones. The present invention is directed to chemistries, methods, and apparatuses which exploit this type of radiation interaction, and to the materials which result from such interactions. The present invention is also directed toward the time dependent behavior of functionalized carbon nanotubes in such composite systems.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/536,688, filed May 27, 2005, which is a national phase entryof International Application No. PCT/03/38141, which claims priority toU.S. Provisional Application Ser. No. 60/429,642, filed Nov. 27, 2002,each of which is hereby incorporated herein by reference.

This work was supported by a small business innovative research (SBIR)awarded by the National Aeronautics and Space Administration (NASA),grant number NAS2-02102; a NASA Cooperative Agreement, grant numberNCC-1-02038 (URETI); and the Robert A. Welch Foundation, grant numberC1494.

TECHNICAL FIELD

The present invention relates generally to materials, and morespecifically to composite or blended materials comprising carbonnanotubes, and said materials' interactions with radiation.

BACKGROUND INFORMATION

Since the discovery of carbon nanotubes in 1991 [Iijima, Nature, 354,pp. 56-58, 1991] and single-wall carbon nanotubes in 1993 [Iijima etal., Nature, 363, pp. 603-605, 1993; Bethune et al., Nature, 363, pp.605-607, 1993], research has been conducted to exploit their uniquemechanical, electrical, and thermal properties to create multifunctionalcomposite materials [Barrera, J. of Mater., 52, pp. 38-42, 2000].Previous research has shown that single-wall carbon nanotubes have thehighest conductivity of any known fiber [Thess et al., Science, 273, pp.483-487, 1996], a higher thermal conductivity than diamond [Hone et al.,Appl. Phys. Lett., 77, pp. 666-668, 2000], and the highest stiffness ofany known fiber [Yu et al., Phys. Rev. Lett., 84, pp. 5552-5555, 2000.

Due to the provocative geometry and other remarkable properties ofcarbon nanotubes, they are of considerable interest to the aerospace andradiation communities [O'Rourke, J. Mater. Res., 17(10), 2002; Klimov etal., Physics Letters A, 226, pp. 244-252, 1997; Cui et al., PhysicsLetters A, 295, pp. 55-59, 2002; Salonen et al., Nuclear Instruments andMethod in Physics Research B, 193, pp. 603-608, 2002]. The possibilityof nanotubes serving as a storage medium for hydrogen [Ye et al., Appl.Phys. Lett, 74(16), pp. 2307-2309, 1999] is of particular interest forfuture spacecraft (e.g., fuel cells), and hydrogen-rich and other lowatomic mass materials are believed to minimize radiation exposure inspace environments [Wilson et al. (Eds.), Shielding Strategies for HumanSpace Exploration, NASA Conference publication 3360, pp. 17-28, 1997].

Efforts to exploit carbon nanotube properties invariably rely on theability to manipulate and homogeneously disperse carbon nanotubes inother host materials and/or matrices. Such manipulability can befacilitated by chemical modification of the carbon nanotube ends [Liu etal., Science, 280, pp. 1253-1256, 1998; Chen et al., Science, 282, pp.95-98, 1998] and/or sidewalls [Bahr et al., J. Am. Chem. Soc., 123, pp.6536-6542, 2001; Holzinger et al., Angew. Chem. Int. Ed., 40(21), pp.4002-4005, 2001; Khabashesku et al., Acc. Chem. Res., 35, 1087-1095,2002] of the carbon nanotubes. However, for many applications, such asthose requiring highly conductive carbon nanotubes, the chemicallymodified or functionalized carbon nanotubes are unsuitable for the finalproduct. Current techniques of chemically [Mickelson et al., J. Phys.Chem. B, 103, pp. 4318-4322, 1999] and thermally [Boul et al., Chem.Phys. Lett., 310, pp. 367-372, 1999; Bahr et al., J. Am. Chem. Soc.,123, pp. 6536-6542, 2001] defunctionalizing functionalized carbonnanotubes place severe restrictions on the types of other materials usedin the various substrates, devices, and composite/blended materialsoriginally comprising the functionalized carbon nanotubes.

SUMMARY

The present invention is directed toward methods of incorporatingfunctionalized carbon nanotubes into host matrices to form compositesand/or blends. In some embodiments, these host matrices are polymeric.In some embodiments, these functionalized carbon nanotubes arefluorinated. In some embodiments, functionalized carbon nanotubes arealigned within the composite and/or blend. The present invention is alsodirected toward methods of removing functional species (e.g., fluorine)from functionalized carbon nanotubes within such composites or blendsvia a radiative means.

The present invention is also directed toward methods ofradiatively-modifying carbon nanotube composites and/or blends. In someembodiments, this comprises a curing process. In some embodiments, thiscomprises a hardening process. In some embodiments, this leads to theformation of hybrid systems wherein carbon nanotubes are effectivelycrosslinked with a polymeric host material, wherein radiation effectsthe necessary crosslinking processes.

In some embodiments, radiation interaction with functionalized carbonnanotube composites and/or blends leads to a defunctionalization of thefunctionalized carbon nanotubes. In some embodiments thisdefunctionalization is selective. In some embodiments, thisdefunctionalization converts the non-conductive functionalized carbonnanotubes into conductive non-functionalized carbon nanotubes.

The present invention is directed to apparatuses comprising carbonnanotubes incorporated into, or housed within, a host matrix, andmethods for making same. In some embodiments, the host matrix ispolymeric. In some embodiments, conductive carbon nanotube channelsexist within a block or film of material comprising nonconductivefunctionalized carbon nanotubes. In some embodiments, lithographictechniques are employed to generate said conductive carbon nanotubechannels by, for example, lithographically defunctionalizingfunctionalized carbon nanotubes. In some embodiments, free-formextraction methods are used to generate three-dimensional arrays ofconductive carbon nanotube channels within a composite or blendedmaterial. The present invention is also directed toward radiationsensors (e.g., dosimeters) comprising functionalized carbon nanotubes ina host material matrix.

The present invention is directed toward multi-functional materialscomprising functionalized carbon nanotubes and a host material, whereinsaid materials' function changes as it exposed to radiation over aperiod of time—continuously changing the properties of the compositeand/or blend material.

The present invention is also directed toward methods of recapturing orrecycling nanotubes from composites and/or blends comprisingfunctionalized carbon nanotubes and a polymer host matrix.

The foregoing has outlined rather broadly the features of the presentinvention in order that the detailed description of the invention thatfollows may be better understood. Additional features and advantages ofthe invention will be described hereinafter which form the subject ofthe claims of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 depicts Raman spectra of (a) pre- and (b) post-irradiation of1.5% wt. Fluorinated Tubes@Rice SWNTs/MDPE;

FIG. 2 depicts Raman spectra of (a) pre- and (b) post-irradiation of 5%wt. and (c) pre- and (d) post-irradiation of 1.5% fluorinated HiPcoSWNTs/MDPE;

FIG. 3 depicts Raman spectra of (a) pre- and (b) post-irradiation of1.5% and (c) pre- and (d) post-irradiation of 5% wt. non-fluorinatedHiPco SWNTs/MDPE; and

FIG. 4 depicts TGA results for the composites containing 5 wt. % F-SWNTs(dashed lines) and 5 wt. % purified SWNTs (solid lines), before (a) andafter (b) irradiation.

DETAILED DESCRIPTION

The present invention is directed toward carbon nanotube compositesand/or blends, and to methods for making such composites and/or blends.The present invention also involves the interaction of radiation withfunctionalized carbon nanotubes that have been incorporated into hostmaterials (e.g., composites and/or blends). The present invention istherefore also directed to chemistries, methods, and apparatuses whichexploit this type of radiation interaction, and to the materials whichresult from such interactions.

The present invention provides for processes that uniformly dispersecarbon nanotubes in other host materials. The present invention providesfor polymer composites and/or blends comprising unroped individualcarbon nanotubes (CNTs) dispersed throughout a polymer host matrix, andmethods for making same. The present invention provides for methods ofpreparing CNT-polymer composites and/or blends wherein interactionsbetween the CNTs and a polymer host can be induced and/or altered byradiation exposure. The present invention provides for a material systemthat can be altered by radiation in both terrestrial and spaceenvironments. The present invention provides for a method of preparingcontinuous fibers comprising CNTs in situ to the fiber making processand where radiation exposure can be used to alter the fiber chemistry inorder to engineer into said fibers desired properties. The presentinvention provides methods of making multifunctional materials withCNTs, wherein radiation exposure is used to impart property changes orenhancements. The present invention provides for methods of preparingcoating systems of which CNTs are a component and wherein radiation canbe used to impact changes to the coating or to selected regions of thecoating. The present invention provides for methods of making plasticparts and panels wherein the properties of the part can vary based uponwhere and how long they have been exposed to radiation. The presentinvention provides for methods wherein CNT-polymer composite circuitboards can be made. In such embodiments, CNT alteration induced byselective radiation exposure can generate electronic devices. In suchembodiments, templating on a polymer substrate can be carried out inorder to enhance electrical conduction or create variations in thematerial's electrical properties in specific regions. The presentinvention also provides for time-dependent multi-functional materialscomprising functionalized CNTs and a polymeric host, wherein saidmaterials' function changes as it is exposed to radiation over a periodof time. Furthermore, the present invention also provides a method ofreclaiming or recycling the CNTs from the CNT-composites and/or blendsat the end of their life cycle.

Carbon nanotubes (CNTs), according to the present invention, include,but are not limited to, single-wall carbon nanotubes (SWNTs), multi-wallcarbon nanotubes (MWNTs), double-wall carbon nanotubes, buckytubes,fullerene tubes, tubular fullerenes, graphite fibrils, carbon whiskers,vapor grown carbon fibers, and combinations thereof. Such carbonnanotubes can be made by any known technique including, but not limitedto, arc discharge [Ebbesen, Annu. Rev. Mater. Sci., 24, pp. 235-264,1994], laser oven [Thess et al., Science, 273, pp. 483-487, 1996], flamesynthesis [Vander Wal et al., Chem. Phys. Lett., 349, pp. 178-184,2001], chemical vapor deposition [U.S. Pat. No. 5,374,415], wherein asupported [Hafner et al., Chem. Phys. Lett., 296, pp. 195-202, 1998] oran unsupported [Cheng et al., Chem. Phys. Lett., 289, pp. 602-610, 1998;Nikolaev et al., Chem. Phys. Lett., 313, pp. 91-97, 1999] metal catalystmay also be used, and combinations thereof. In some embodiments, theCNTs are separated based on a property selected from the groupconsisting of chirality, electrical conductivity, thermal conductivity,diameter, length, number of walls, and combinations thereof. SeeO'Connell et al., Science, 297, pp. 593-596, 2002; Bachilo et al.,Science, 298, pp. 2361-2366, 2002; Strano et al., Science, 301, pp.1519-1522, 2003; all of which are incorporated herein by reference. Insome embodiments, the CNTs have been purified. Exemplary purificationtechniques include, but are not limited to, Chiang et al., J. Phys.Chem. B, 105, pp. 1157-1161, 2001; Chiang et al., J. Phys. Chem. B, 105,pp. 8297-8301, 2001, both of which are incorporated herein by reference.In some embodiments, the CNTs have been cut by a cutting process. SeeLiu et al., Science, 280, pp. 1253-1256, 1998; Gu et al., Nano Lett.,2(9), pp. 1009-1013, 2002, both of which are incorporated by reference.In some embodiments, the CNTs are crosslinked with each other (e.g., byshear pressure).

In some embodiments of the present invention, the carbon nanotubes arefunctionalized. Functionalization includes, but is not limited to,fluorination. For examples of suitable functionalized CNTs and methodsof functionalizing CNTs, see Mickelson et al., Chem. Phys. Lett., 296,pp. 188-194, 1998; Bahr et al., J. Am. Chem. Soc., 123, pp. 6536-6542,2001; Holzinger et al., Angew. Chem. Int. Ed., 40(21), pp. 4002-4005,2001; Khabashesku et al., Acc. Chem. Res., 35, pp. 1087-1095, 2002;Mickelson et al., J. Phys. Chem. B, 103, pp. 4318-4322, 1999; Boul etal., Chem. Phys. Lett., 310, pp. 367-372, 1999; Bahr et al., Chem.Mater., 13, pp. 3823-3824, 2001; Stevens et al., Nano Lett., 3(3), pp.331-336, 2003; Pekker et al., J. Phys. Chem. B, 105, pp. 7938-7943,2001; all of which are incorporated herein by reference.

Host materials into which functionalized CNTs are incorporated include,but are not limited to, metals, ceramics, semiconductors, sol-gels,alloys, metalloids, polymers, fluids, oils, waxes, solvents, andcombinations thereof. In some embodiments, functionalized CNTs areincorporated into ceramic hosts in a manner similar to that described incommonly-assigned, co-pending U.S. patent application Ser. No.10/366,183, filed Feb. 13, 2003.

Polymeric host materials, as described herein, include, but are notlimited to, thermoplastics, thermosets, co-polymers, elastomers,silicones, fluorinated polymers, epoxies, and combinations thereof. Insome embodiments, said polymeric host materials comprise additives,which include, but are not limited to, plasticizers, curing agents,catalysts, and combinations thereof.

The present invention is directed toward methods of incorporatingfunctionalized CNTs into polymer matrices to form CNT-polymer compositesand/or blends. This is typically done by 1) dispersing functionalizedCNTs in a solvent to form a dispersion, 2) adding the dispersion topolymer material of suitable form using an incipient wetting process, 3)removing the solvent to form functionalized CNT-covered polymerparticulates, and 4) blending the functionalized CNT-covered polymerparticulates at a temperature in excess of the melting point of thepolymer used.

In some embodiments, these functionalized CNTs are fluorinated CNTs(F-CNTs). In some embodiments of the present invention, fluorinationand/or additional/other functionalization is used to achieve dispersionsof unbundled CNTs in materials, wherein the CNTs are unroped and largelyseparated. In some embodiments, the solvent is selected from the groupconsisting of alcohols, N,N-dimethylformamide, benzene, toluene, xylene,dichlorobenzene, chloroform, dichloromethane, and combinations thereof.Polymer material of suitable form, according to the present invention,includes, but is not limited to, particles, fibers, and combinationsthereof. Fibers include, but are not limited to, weaves, rowing, tows,mats, and combinations thereof. In some embodiments, functionalized CNTsare aligned (e.g., by shearing action) within the composite and/orblend. Rapid prototyping, for example, can effect this type of alignmentby its extrusion process.

Fluorination of CNTs, for example, can facilitate the unroping ofsingle-wall carbon nanotubes from nanotube ropes or bundles. Processingof fluorinated carbon nanotubes (F-CNTs) in polymers can lead todispersions of F-CNTs in the polymer. In many cases, these dispersionscomprise highly dispersed individually unroped CNTs (this isparticularly true for SWNTs—which have a strong propensity toagglomerate into bundles and/or ropes). Raman spectroscopy can be usedto study these dispersions and show that the fluorinated carbonnanotubes can maintain their fluorinated condition even afterprocessing. In some embodiments, the fluorinated carbon nanotubes arefurther functionalized, as described in Boul et al., Chem. Phys. Lett.,310, pp. 367-372, 1999, and incorporated herein by reference.

In some embodiments, the polymer host may be generated (i.e.,polymerized from monomeric precursors) within, or in the midst of, thedispersion of functionalized CNTs. In some embodiments thefunctionalized CNTs are dispersed in a solution comprising polymericprecursors. In some embodiments, such as those utilizing an epoxy hostmaterial, the functionalized CNTs are added prior to any curing events,and they can be incipient wet to the starting fiber system.

Functionalized CNTs are generally added in a quantity which ranges fromabout 0 wt. % to about 99 wt. %, and more typically from about 0.2 wt. %to about 50 wt. % (of the total CNT-composite and/or blend).

The present invention is also directed toward methods ofradiatively-modifying carbon nanotube composites or blends. In someembodiments, this comprises a curing process. In some embodiments, thiscomprises a hardening process. In some embodiments, this leads to theformation of hybrid systems wherein carbon nanotubes are effectivelycrosslinked with a polymeric host material, wherein radiation effectsthe necessary crosslinking processes. In some embodiments of the presentinvention, radiation exposure leads to an alteration of the propertiesof F-CNTs and other functionalized CNTs within a polymer host materialby effecting reaction, further curing, crosslinking, bonding, oroxidation of the nanotubes in situ within the polymer host or matrixsystem. In some embodiments, radiation is used to defunctionalize thedefunctionalized CNTs. In some of these latter embodiments, thisliberates species from the nanotube into a controlled environment.

Radiation, according to the present invention, includes, but is notlimited to, electromagnetic radiation, particle radiation, andcombinations thereof. Exemplary forms of such radiation include, but arenot limited to, ultraviolet (UV), infrared (IR), X-ray, gamma ray(γ-ray), protons (H⁺), neutrons, electrons, alpha particles(α-particles), heavy ions, cosmic radiation, solar wind, andcombinations thereof. Cosmic radiation, according to the presentinvention, includes, but is not limited to, ions, ranging in size fromhydrogen to uranium, that have been accelerated to extremely highenergies.

Using fluorinated CNTs to impart specified nanotube conditions within apolymer (e.g., a high degree of dispersion), and using radiation sourcesor radiation in space to alter, remove, react, or further functionalizethe nanotubes in an effort to provide a range of properties thatinclude, but are not limited to, radiation protection, enhancedstrength, improvements in electrical and thermal properties, andcombinations thereof, that can ultimately lead to multifunctionalnanocomposites and hybrid systems. In some embodiments of the presentinvention, radiation is used to alter the chemistry of the nanotubes inpolymer composites, hybrids and other material systems. In someembodiments, radiation exposure of a CNT-polymer composite and/or blendmaterial can lead to a hardened surface or skin condition.

From analysis of Raman spectra, F-CNTs within polyethylene host matriceswere observed to revert back to unfluorinated CNTs when exposed toradiation. While not intending to be bound by theory, the process islikely a defluorination of the F-CNTs, a promotion of H—F bonding at theexpense of C—F bonding, a lowering of the nanotube surface energy, anincrease in electron charge or electron flow that would drive thedebonding of the fluorine at energy levels much lower than a thermallyassisted reverse process from F-CNTs back to unfluorinated CNTs, or acombination of any or all of these mechanistic scenarios.

The present invention is directed to apparatuses comprising CNTs housedwithin a polymeric matrix, and methods for making same. In someembodiments, conductive (metallic, semi-metallic, and/or semiconducting)carbon nanotube channels exist within a block or film of materialcomprising nonconductive functionalized carbon nanotubes. Suchapparatuses include, but are not limited to, circuit boards, sensors,micro-electrical mechanical systems (MEMS), nano-electrical mechanicalsystems (NEMS), and combinations thereof.

In some embodiments, lithographic techniques are employed to generateconductive carbon nanotube channels within functionalized CNT-polymercomposite layers. This is accomplished by using radiation to selectively(lithographically) remove functional groups from the functionalizedcarbon nanotubes rendering them conductive only in the regions in whichthe functionalization has been removed. In some embodiments, however,the functional groups and level of functionalization is carefully chosenso that the functionalized CNTs are partially- or semi-conducting.Lithographic removal of such functionalization then creates regions ofhigh conductivity and semiconductivity in a dielectric matrix. Suchlithographic techniques may comprise any type of electromagnetic and/orparticulate radiation. Exemplary lithographic techniques include, butare not limited to, optical lithography, UV lithography, deep-UVlithography, X-ray lithography, scanning near-field optical lithography,electron-beam lithography, ion-beam lithography, proton-beamlithography, and combinations thereof. In some embodiments, a photomaskis employed as part of the lithographic technique. In some embodiments,free-form extraction methods are used in concert with theabove-mentioned lithographic techniques to generate three-dimensionalarrays of conductive carbon nanotube channels within a composite orblended material.

The present invention is also directed toward radiation sensors (e.g.,dosimeters) comprising the functionalized CNTs-polymeric compositeand/or blend materials of the present invention. In some embodiments,the functionalized CNT-polymer composite is present in the form of alayer which can range in thickness from about 10 nm to about 10 mm. Asthe sensor is exposed to radiation that defunctionalizes thefunctionalized CNTs, there is a net change in the electrical properties(e.g., conductance, conductivity, resistance, and resistivity) of thematerial, which can be measured with a device such as a multimeter, avoltmeter, a four-point electrical probe, and combinations thereof. Withcalibration and a thorough understanding of the interactions ofparticular kinds of radiation with a particular type of functionalizedCNT, it is possible to monitor radiation dosages and fluences in realtime. The sensor components are easily miniaturized such that the devicecan be worn by a person as a radiation badge. This offers manyadvantages to traditional radiation badges which must be sent out foranalysis, informing the person wearing the sensor of a large dose ofradiation only after the fact.

The present invention is also directed toward multi-functional materialscomprising functionalized CNTs and a polymeric host, wherein saidmaterials' function changes as it is exposed to radiation over a periodof time—continuously changing the properties of the materials. In someembodiments, for example, a functionalized CNT-polymer composite mightbecome a better radiation shield as it is irradiated.

The present invention is also directed toward methods of recapturing orrecycling nanotubes from composites and/or blends comprisingfunctionalized carbon nanotubes and a polymer host matrix.

The present invention is useful for the preparation of CNT-reinforcedcomposites and CNT-polymer hybrids. The use of radiation exposure,either in a manufacturing process or while in outer space, can furtherprocess the composites to alter the properties of the composite bydesign. The present invention can provide for multifunctional CNTsand/or CNT composites and/or blends. The present invention may be usedto reverse properties and or heal unwanted properties and damage. Somerepresentative applications for the present invention are describedbelow.

Multifunctional composites that are altered in space for space station,shuttle, satellites, and deep space spacecraft. A manner of impartingchange or repair to spacecraft that involves radiation from space andlittle or no additional energy requirements to do so.

Materials that provide for improved shielding and/or provide for therelease of desired outgassing that could act as a fuel source (e.g.,fuel cells) or a means of providing an oxygen source.

Materials for new electronic devices and circuitry. Through the use ofradiation of fluorinated or other functionalized nanotubes withinpolymer composites or blends, electronic devices can be made. Circuitboards can be made with circuitry down to nanoscale. Circuit boards orchip assemblies could be patterned via radiation exposure to produceregions that are conducting and/or semiconducting, amidst insulatingand/or semiconducting regions. Additionally, radiation could be used toeffect the device operation (nanoelectronics).

Materials systems with surfaces or coatings having enhanced mechanicalproperties and which are generated by radiation exposure of materialscomprising functionalized nanotubes within a polymer host. Suchradiatively-induced nanotube chemistry has the capacity to impactbonding and load transfer.

Use of radiation exposure to impact nanotubes in fluids. In suchapplications, nanotubes can be radiatively-altered to induce changes inthe fluid which range from changes in solubility level to improvedelectrical and thermal properties. In some embodiments, these changescould be made to be time-dependent and/or occur over a period of time.The chemistry could be altered to allow for more favorable fluidconditions (e.g., viscosity) for a number of applications. This may alsoprovide a method of producing nanotubes dispersed in a fluid for asubsequent use. In such cases, as the nanotubes are exposed to theradiation they (a) become defluorinated as single unroped nanotubes, (b)lose the functionalization in a manner similar to (a), thefunctionalization is altered when interacted with the fluid, or (c) thenanotubes in a fluid are reacted to form a continuous network throughcross-linking and nanotube-to-nanotube linking.

There are clearly numerous applications for CNT-polymer compositesand/or blends. The present invention provides a method for promotingproperty enhancement via radiation exposure from a variety of sourcescovering a broad range of radiation. The present invention provides fora straightforward and commercially scalable method for enhancing theproperties of CNT-polymer nanocomposites and/or blends. The presentinvention provides new routes to composite systems not yet fullyidentified and opens new doors to the use of nanotubes in electronicapplications. The present invention also facilitates the development ofnew structural composites and multifunctional CNT materials.

The following examples are included to demonstrate particularembodiments of the present invention. It should be appreciated by thoseof skill in the art that the methods disclosed in the examples whichfollow merely represent exemplary embodiments of the present invention.However, those of skill in the art should, in light of the presentdisclosure, appreciate that many changes can be made in the specificembodiments described and still obtain a like or similar result withoutdeparting from the spirit and scope of the present invention.

EXAMPLES Example 1

This Example serves to illustrate embodiments in which medium energyprotons can be used to modify the properties of fluorinated CNT-polymercomposites and/or blends.

As long term space-based experiments are not a practical way ofaccessing the radiation characteristics of materials, SWNT-polymercomposites were irradiated with 40 MeV protons at the Texas A&MUniversity Cyclotron Institute (TAMCI). The proton energies and thetotal particle fluence used in this example are consistent with theradiation environment of low earth orbit (LEO); such as the environmentencountered by the International Space Station (ISS). To characterizethe effects of proton irradiation on CNTs, the samples werecharacterized by thermogravimetric analysis (TGA) and Ramanspectroscopy.

The SWNTs used in this example were obtained from Tubes@Rice and CarbonNanotechnologies, Inc, both in purified form. These nanotubes wereproduced by the pulsed laser vaporization [Rinzler et al., Appl. Phys.A., 67, pp. 29-37, 1998] and High Pressure Carbon Monoxide (HiPco)[Bronikowski et al., J. Vac. Sci. & Tech. A, 19, pp. 1800-1805, 2001]processes, respectively. The CNT-polymer composites were prepared withSWNTs made by each method and with fluorinated SWNTs (F-SWNTs)comprising SWNTs made by each method. The fluorination of the SWNTs wasperformed by previously described methods [Mickelson et al., Chem. Phys.Lett., 296, pp. 188-194, 1998; Chiang et al., “Covalent SidewallFunctionalization of Single Wall Carbon Nanotubes,” presented at AppliedDiamond Conference/Second Frontier Carbon Joint Conference Proceedings2001; Gu et al., Nano. Lett., 2(9), pp. 1009-1013, 2002; all of whichare incorporated herein by reference], and comprising a stoichiometry ofapproximately C₂F. Medium density polyethylene (MDPE) was obtained fromAldrich in powder form to create the composites. The MDPE had amolecular weight of 6000 and a melting point between 109-111° C. Thecomposite compositions studied are found in Table 1.

The composites were processed by incipient wetting followed by Banburymixing. The incipient wetting technique creates an initial level ofdispersion by coating the polymer with nanotubes [Barrera, J. Mater.,52, pp. 38-42, 2000; Cooper et al., Composites Sci. & Tech., 62, pp.1105-1112, 2002]. A polymer powder and a nanotube solution were combinedand heated in an oil bath to remove the solvent. The remaining materialwas dried in a furnace to remove the remaining solvent. The overcoatedpolymer was subsequently processed by Banbury mixing and pressed intosheets by heated compression molding. The unfilled polymer was processedin the same manner for consistency.

Each composite sample was placed between two sheets of thin Mylar™ tofacilitate positioning in the proton beam. The samples were irradiatedwith 40 MeV protons at a flux rate of about 1.7×10⁷ protons per cm² persecond to a total fluence of 3×10¹⁰ protons/cm² (except in one case).The fluence was chosen to be consistent with the expected exposureduring a long-term LEO mission. The irradiations were performed at roomtemperature in a vacuum of about 5×10⁻⁵ Torr. The irradiation conditionsfor the samples are summarized in Table 1.

TABLE 1 Samples studied and radiation conditions. Sample Fluence 1.5%wt. SWNT/MDPE (purified HiPco) 3 × 10¹⁰ protons/cm²   5% wt. SWNT/MDPE(purified HiPco) 3 × 10¹⁰ protons/cm² 1.5% wt. F-SWNT/MDPE (laserTubes@Rice) 3 × 10¹⁰ protons/cm²   5% wt. F-SWNT/MDPE (HiPco) 3 × 10¹⁰protons/cm² 1.5% wt. F-SWNT/MDPE (HiPco) 4.7 × 10¹⁰ protons/cm²   MDPE 3× 10¹⁰ protons/cm²

The samples were characterized before and after irradiation by Ramanspectroscopy. The Raman spectroscopy measurements utilized a RenishawMicro-Raman spectrometer with 780.6 nm diode laser excitation and aresolution of 2 cm⁻¹. The objective used was 50× with a 0.55 μmaperture. In addition, pieces of each sample were used to perform TGA.Samples were studied both before and after irradiation. TGA wasperformed in a nitrogen atmosphere to ascertain whether radiationexposure may have caused any damage to the polymer. The apparatus usedwas a TA Instruments Model SDT 2960. Weight loss and temperaturedifference values were used to evaluate the materials.

The Raman spectroscopy results suggested that the proton radiation hadless of an effect on the fluorinated laser-generated SWNTs than on thefluorinated HiPco-produced SWNTs, as seen in FIGS. 1-3. The significantfeatures of the pre-irradiation Raman spectra of the laser-generatedF-SWNT's (Tubes@Rice) in FIG. 1, are still seen in the spectrapost-irradiation. The fluorinated HiPco tubes appeared to defluorinateafter radiation because the Raman spectra resemble non-fluorinated HiPcotubes post-radiation as seen in FIG. 2. The non-fluorinated SWNTs showedno remarkable change on going from pre- to post-irradiation, as seen inFIG. 3. The difference in percentage weight loss of the 1.5 wt. % and 5wt. % SWNT loadings showed negligible differences between the pre- andpost-irradiation for both the fluorinated and non-fluorinated SWNTs. TheRaman spectra of a control sample of unfilled PE showed no significantchange after irradiation.

The TGA results in FIG. 4, show that no detrimental changes in thethermal degradation properties of the unfilled polymer or the compositesoccurred due to radiation exposure. All samples decomposed in one stepwith the maximum weight loss occurring at a temperature between 469° C.and 479° C. The composite comprising purified, unfunctionalized SWNTsand fluorinated Tubes@Rice-produced SWNTs did not show any appreciablechange at the temperature where this peak occurred, but the peakposition for the composites containing fluorinated HiPco SWNTs shiftedto a higher temperature. In both the 1.5 wt. % and 5 wt. % F-SWNTcomposites, the inflection point shifted approximately 4° C. tocorrespond with their purified SWNT counterparts corroborating thedefluorination observed in the Raman spectra. FIG. 4 shows the percentweight loss curves and the derivative percent weight loss curves in theinset plotted against temperature for the composites containing 5 wt. %purified SWNTs and 5 wt. % F-SWNTs. The curves for the other materials;unfilled polyethylene, 1.5 wt. % F-SWNT (Tubes@Rice)/MDPE, 1.5 wt. %purified SWNT/MDPE, and 5 wt. % purified SWNT/MDPE; agreed within onedegree, indicating that no radiation-induced damage occurred in thesematerials.

FIG. 4 depicts the TGA results for the composites containing 5 wt. %F-SWNTs (dashed lines) and 5 wt. % purified SWNTs (solid lines). Theleft graph shows the TGA data for the composite materials prior toradiation exposure and the right graph shows the TGA data for thematerials following radiation exposure. The curves for the compositecontaining F-SWNTs shift to higher temperatures following radiationexposure suggesting that the fluorine functional groups are removed bythe radiation.

These results indicate that radiation exposure with 40 MeV protonsinduces defluorination of the HiPco SWNTs, as evidenced in the Ramanspectra and by TGA results. The proton exposures were consistent with along-term mission in LEO. This is significant since it would serve as abasis to explore future applications of SWNTs in space. A similar effectis not observed in the fluorinated Tubes@Rice SWNTs. While not intendingto be bound by theory, this suggests that the diameter and curvature ofthe CNTs and the conditions under which they are functionalized play arole in any radiation-induced defunctionalization process they might besubjected to. Therefore materials can be manipulated such that they aredefunctionalized on demand to produce CNTs with an altered level and/ortype of functionalization.

Example 2

This Example serves to illustrate a manner in which a sensor of thepresent invention comprising functionalized CNTs and a polymer hostmatrix can be used as a radiation dosimeter.

The present invention is directed toward radiation sensors (e.g.,dosimeters) comprising functionalized CNTs in a polymeric host material.In some embodiments, such a device comprises a dielectric substrate onwhich a layer of functionalized CNT-polymer composite and/or blend isdeposited. Using a power source, a voltage can be applied across thislayer. As the device is exposed to radiation that defunctionalizes thefunctionalized CNTs, there is an increase in current across the layer.With calibration and a thorough understanding of the interactions ofparticular kinds of radiation with a particular type of functionalizedCNT, it is possible to monitor radiation dosages and fluences in realtime. The device components are easily miniaturized such that the devicecan be worn by a person as a radiation badge. This offers manyadvantages to traditional radiation badges which must be sent out foranalysis, informing the wearing of a large dose of radiation only afterthe fact. Other variants of these radiation sensors are not worn byindividuals, rather they are used to simply monitor a particularenvironment or environments for radiation. In some embodiments, suchradiation sensors can be incorporated into the hull of a spacecraft,often sensing different kinds of radiation, at differing depths in orderto evaluate both the type and dosage of various types of incidentradiation. In some embodiments, the sensor can be made using ink jetmethodologies to reduce the device size and ensure alignment (orrandomness) of the CNTs within the host matrix.

Example 3

This Example serves to illustrate multi-functional materials of thepresent invention, comprising functionalized CNTs and a host material,that can be used in time-dependent applications.

Embodiments directed toward multi-functional materials comprisingfunctionalized CNTs and a host material often rely on changes in saidmaterials as they are exposed to radiation over a period oftime—continuously changing the properties of the materials.

As an example, functionalized CNTs dispersed in motor oil could beengineered to impart gradual changes to the viscosity of such a fluidwhen exposed to a particular type of radiation. This would permit thetuning of the oil's viscosity in situ, without having to change it.Furthermore, after having altered the oil's viscosity to a sufficientextent, the oil could be used for an entirely different purpose.Additionally, or alternatively, such time-dependent behavior could bemade to respond to other environmental input (e.g., heat, pressure,stress, etc.).

Example 4

This Example serves to illustrate how interactions of functionalizedCNT-polymer composites and/or blends of the present invention withradiation can be employed to recycle or reclaim the CNTs as the deviceor material comprising them nears the end of its life.

Because CNTs are still relatively difficult to produce and have acorresponding high cost associated with them, it may be advantageous insome situations to somehow reclaim them at some point. Thus, the presentinvention is also directed toward methods of recapturing or recyclingnanotubes from composites and/or blends comprising functionalized carbonnanotubes and a polymer host matrix.

For functionalized CNTs in a polymer matrix (e.g., polyethylene),reclaiming the CNTs involves both their separation from the polymermatrix and their defunctionalization. Because of the high level ofchemical inertness the CNTs possess, the polymer matrix can bechemically dissolved with an appropriate solvent (e.g.,tetrahydrofuran), it can be oxidatively removed with an oxidizing agent(e.g., sulfuric acid), or burned in oxygen. The functionalized CNTs canbe defunctionalized either before or after separation from the polymermatrix using a radiative means capable of removing saidfunctionalization. The combination of these two processes yields aunfunctionalized CNT product. Note that in some embodiments, thedefunctionalization occurs as a result of a material's use (e.g., in aspace environment) and subsequent matrix removal serves to complete therecycling process. These processes can be engineered into the materialso that the process occurs over an extended time in an effort to reclaimthe material (CNTs) rather than for them to go into landfills.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims.

1. A method comprising the steps of: a) dispersing functionalized carbonnanotubes in a solvent to form a dispersion of functionalized carbonnanotubes; b) incorporating the dispersion of functionalized carbonnanotubes into a polymer host matrix to form a functionalized carbonnanotube-polymer composite; and c) modifying the functionalized carbonnanotube-polymer composite with radiation, wherein the modifyingcomprises effecting a modification of the carbon nanotubes in situwithin the polymer host matrix, wherein the modification is selectedfrom the group consisting of crosslinking, curing, vulcanization,hardening, bonding, oxidation, and combinations thereof.
 2. The methodof claim 1, wherein the carbon nanotubes are single-wall carbonnanotubes.
 3. The method of claim 1, wherein the functionalized carbonnanotubes are fluorinated carbon nanotubes.
 4. The method of claim 1,wherein the dispersion is formed with a solvent selected from the groupconsisting of alcohols, N,N-dimethylformamide, benzene, toluene, xylene,dichlorobenzene, chloroform, dichloromethane, and combinations thereof.5. The method of claim 1, wherein the step of incorporating thedispersion of functionalized carbon nanotubes into a polymer host matrixcomprises an incipient wetting of polymer material, of a form selectedfrom the group consisting of particles, fibers, and combinationsthereof, followed by solvent removal and blending.
 6. The method ofclaim 1, wherein the step of incorporating the dispersion offunctionalized carbon nanotubes into a polymer host matrix comprisesmixing the dispersion with polymeric precursors and polymerizing insitu.
 7. The method of claim 1, wherein functionalized carbon nanotubescomprise from about 0.001 weight percent to about 99 weight percent ofthe functionalized carbon nanotube-polymer composite.
 8. The method ofclaim 1, wherein functionalized carbon nanotubes comprise from about 0.2weight percent to about 30 weight percent of the functionalized carbonnanotube-polymer composite.
 9. The method of claim 1, wherein the stepof modifying the functionalized carbon nanotube-polymer composite withradiation comprises radiation selected from the group consisting ofultraviolet radiation, infrared radiation, X-ray radiation, gamma-rayradiation, protons, neutrons, electrons, alpha particles, heavy ions,cosmic radiation, solar wind, and combinations thereof.
 10. The methodof claim 1, wherein the modification comprises crosslinking.
 11. Themethod of claim 10, wherein the crosslinking comprises crosslinking thefunctionalized carbon nanotubes with each other.
 12. The method of claim10, wherein the crosslinking comprises crosslinking the functionalizedcarbon nanotubes with the polymer host matrix.
 13. The method of claim1, wherein the modification comprises curing.
 14. The method of claim 1,wherein the modification comprises curing.
 15. The method of claim 1,wherein the modification comprises vulcanization.
 16. The method ofclaim 1, wherein the modification comprises hardening.
 17. The method ofclaim 16, wherein the hardening comprises surface hardening.
 18. Themethod of claim 1, wherein the modification comprises bonding.
 19. Themethod of claim 1, wherein the modification comprises oxidation.